| 拉脊山口蛇绿混杂岩中辉绿岩的地球化学特征及SHRIMP锆石U-Pb年龄 |
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| 引用本文： | 付长垒,闫臻,郭现轻,牛漫兰,夏文静,王宗起,李继亮.拉脊山口蛇绿混杂岩中辉绿岩的地球化学特征及SHRIMP锆石U-Pb年龄[J].岩石学报,2014,30(6):1695-1706. |
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| 作者姓名： | 付长垒 闫臻 郭现轻 牛漫兰 夏文静 王宗起 李继亮 |
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| 作者单位： | 中国地质科学院地质研究所, 大陆构造与动力学国家重点实验室, 北京 100037;中国地质科学院地质研究所, 大陆构造与动力学国家重点实验室, 北京 100037;中国地质科学院矿产资源研究所, 北京 100037;合肥工业大学资源与环境工程学院, 合肥 230009;合肥工业大学资源与环境工程学院, 合肥 230009;中国地质科学院矿产资源研究所, 北京 100037;中国科学院地质与地球物理研究所, 北京 100029 |
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| 基金项目： | 本文受国家自然科学基金项目（41372207）和中国地质调查局地质调查项目（1212011120159、12120114080001）联合资助. |
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| 摘 要： | 拉脊山口蛇绿混杂岩是分布于中祁连和南祁连构造带之间蛇绿混杂带的重要组成部分。该混杂带中的岩石种类相对齐全，各岩性间为构造接触；其中辉绿岩以岩块和岩墙两种形式产出。辉绿岩块SiO2含量为49.80%~50.13%，MgO含量为5.43%~5.64%，FeOT为10.96%~11.52%，TiO2含量较高（2.38%~2.62%）；辉绿岩墙SiO2含量为43.41%~45.74%，MgO含量为9.04%~10.64%，FeOT为8.39%~9.96%，TiO2含量较低（0.89%~1.02%），二者均属拉斑玄武岩系列。其中辉绿岩块ΣREE为135.4×10-6~150.9×10-6，（La/Yb）N=3.51~4.03，具有右倾型稀土配分模式，富集Rb、Ba、K、Sr等大离子亲石元素及Th、Nb、Ta、Zr、Hf、Ti等高场强元素，呈现洋岛拉斑玄武岩特征；辉绿岩墙ΣREE为36.10×10-6~43.72×10-6，（La/Yb）N=1.12~1.20，稀土配分曲线相对平坦，呈现出与洋中脊玄武岩相似的稀土和微量元素配分模式。这两类辉绿岩样品均缺乏Nb、Ta和Ti负异常，可能分别形成于洋岛/海山和洋中脊环境。SHRIMP锆石U-Pb测年结果显示，辉绿岩块形成时代为491.0±5.1Ma。这些不同构造属性的辉绿岩可能形成于原特提斯洋向北俯冲消减过程。
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| 关 键 词： | 辉绿岩 洋岛/海山 洋中脊 蛇绿混杂岩 拉脊山 |
| 收稿时间： | 2013/1/30 0:00:00 |
| 修稿时间： | 2013/6/24 0:00:00 |
Geochemistry and SHRIMP zircon U-Pb age of diabases in the Lajishankou ophiolitic mélange, South Qilian terrane |
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| FU ChangLei,YAN Zhen,GUO XianQing,NIU ManLan,XIA WenJing,WANG ZongQi and LI JiLiang.Geochemistry and SHRIMP zircon U-Pb age of diabases in the Lajishankou ophiolitic mélange, South Qilian terrane[J].Acta Petrologica Sinica,2014,30(6):1695-1706. |
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| Authors: | FU ChangLei YAN Zhen GUO XianQing NIU ManLan XIA WenJing WANG ZongQi and LI JiLiang |
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| Institution: | State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;Department of Resources and Environment, Hefei University of Technology, Hefei 230009, China;Department of Resources and Environment, Hefei University of Technology, Hefei 230009, China;Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | The Lajishankou ophiolitic mélange, which is an important ingredient of the ophiolitic mélange between the Central and the South Qilian terranes, contains varities of lithological units showing tectonic relationship between them. Diabases in this mélange occur as blocks and dykes respectively. The formers have SiO2 contents of 49.80%~50.13%, MgO contents of 5.43%~5.64%, FeOT contents of 10.96%~11.52% and relatively higher TiO2 contents of 2.38%~2.62%; the laters have SiO2 contents of 43.41%~45.74%, MgO contents of 9.04%~10.64%, FeOT contents of 8.39%~9.96% and low TiO2 contents of 0.89%~1.02%. They belong to tholeiitic rocks. The diabase blocks have high total REE contents (135.4×10-6~150.9×10-6) and (La/Yb)N ratios (3.51~4.03) with right-inclined REE patterns and enrichment in large ion lithophile elements (including Rb, Ba, K, Sr) and high field strength elements (including Th, Nb, Ta, Zr, Hf, Ti), showing typical features of OIB. However, the diabase dykes have low total REE contents (36.10×10-6~43.72×10-6) and (La/Yb)N ratios (1.12~1.20) and flat REE patterns, indicating similar character of MORB. In addition, diabase blocks and dykes are lack of negative Nb, Ta and Ti anomalies. SHRIMP zircon U-Pb dating of diabase block yields a weighted mean 206Pb/238U age of 491.0±5.1Ma, representing the age of crystallization. These characters suggest that the mafic diabases in the Lajishankou ophiolitic mélange were probably formed in ocean island/seamount and mid-ocean ridge environments, which were mixed with other lithological units during the northward subduction-accretion of the Proto-Tethys Ocean. |
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| Keywords: | Diabase Ocean island/Seamount Mid-ocean ridge Ophiolitic mé lange Lajishan Mountain |
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